A digital network comprises of a group of nodes that are connected to each other through a variety or interfaces. The network can also be logically considered to comprise several layers including, for example, a physical layer, a data link layer, a network layer, and a transmission layer. In each of these layers, different agreed upon standards that enable various vendor equipment to communicate may be used. The standards are also known as communications protocols.
Asynchronous Transfer Mode (“ATM”) or “cell switching” is a technology designed for transmitting digital information such as voice, video, and data at high speeds through the digital network. In the ATM protocol, the digital information to be transferred is first arranged into equal sized units called cells having fixed lengths. The cells are then transmitted from node to node until they reach a destination node through a pathway (or connection) within the digital network.
The communication path between two nodes is established through a virtual circuit. In a virtual circuit, the path may be established and then removed, and resources along the path may be shared by multiple virtual circuits. When the data cells are sent through network switches that established virtual circuits through an automated call-setup procedure, the communication paths are called Switched Virtual Circuits (“SVCs”).
The digital network is constructed of digital switches coupled together through digital communication links such as, for example, trunks. The trunks carry the cells of information between the digital switches along the connection. The digital switches route the cells from incoming communication links to outgoing communication links and finally to the destination node.
The ATM protocol can be incorporated into another type of communications protocol, the Transmission Control Protocol/Internet Protocol (“TCP/IP”). The Internet Protocol (“IP”) is used to carry out data transmission at the network layer of the digital network, while the Transmission Control Protocol (“TCP”) is used at the transport layer. A conventional IP network is typically implemented using routers. A message is divided into packets that have variable lengths, unlike the ATM cells described above. Each router receives a packet and determines an output port to which the packet is to be delivered using an IP address attached to that packet. When packets are processed through the router, the packets may not all take the same path or virtual circuit. Processing packets through a router is advantageous when the applications being performed are small in time and/or bandwidth. However, processing becomes difficult and expensive when the applications have larger requirements.